The yen has climbed to a three-month high after Japan and the US carried out a rare joint intervention to support the currency, marking the first such collaboration between the two countries since 2011. The move matters because it signals growing alarm in Washington and Tokyo over the yen's persistent weakness, driven by a gap between Japanese and US borrowing costs, and highlights President Trump's direct involvement in shoring up an ally's currency.

The yen strengthened to ¥155 against the dollar on Monday, up from a 40-year low of nearly ¥164 the previous week, after coordinated yen-buying by both governments. Trump said the US was "always there for Japan", while Treasury secretary Scott Bessent, whose notebook was seen listing a plan to buy $5bn-$10bn of yen, vowed further intervention if needed and repeated calls for the Bank of Japan to raise rates further. Analysts were divided on the outlook: MUFG's Lee Hardman said the threat of more intervention should deter speculators, while Oxford Economics warned the action alone would not reverse the underlying trend of yen weakness, with the BoJ likely to hold off on further rate rises until December.